Why not get modern and throw responses, highlights, and claps into the mix? All of these things indicate engagement. Surely the Medium programmers are clever enough. If you are worried that some people clap without reading just to give a boost to their buds, you could exclude claps for a view as opposed to claps for a read. Similarly you could weight people’s claps according to how generous or stingy that individual happens to be. As I already said, surely the programmers here are clever enough.